Referring to FIG. 1, it shows that a fault current of an asymmetrical fault of a conventional system must be analyzed by use of a symmetrical component method. Specifically, the system is decomposed into a positive, a negative and a zero phase sequence network, and serial and parallel connections of the positive, the negative and the zero phase sequence network are respectively performed according to various types of asymmetrical faults, such as a single line-to-ground (SLG) fault, a two-phase short circuit fault, and a double line-to-ground (DLG) fault, to solve the fault current of the asymmetrical fault. The process is rather cumbersome and time-consuming. Moreover, when a bus or impedance is added to the system, a Jacobian matrix or Y admittance matrix therein must be calculated and analyzed again, and the process is rather complicated, which reduces the execution speed and consumes a great deal of memory space. In addition, the conventional symmetrical component method is mainly applied to a three-phase network, which may be decomposed into three phase sequence networks, that is, a positive, a negative and a zero phase sequence network. However, when the power distribution system is a three-phase and single-phase mixed network, the application of the symmetrical component method is limited, and in actual application, power networks of a majority of microgrid power distribution systems are in a three-phase and single-phase mixed state, so that for the application of a smart instrument, it is necessary to provide an innovative and progressive system fault analysis and identification method, to solve the foregoing problem.
Many applications, such as network optimization, reactive-power planning, feeder reconfiguration, state estimation, short-circuit-analysis etc. are necessary to construct microgrid distribution automation (MGDA) effectively. These are the important tools for improving reliability and efficiency for off-line planning and real time operation of the protective needs of MGDA. A microgrid is made up of large numbers of on-site distributed generators (DGs), which may include microturbine generations (MTGs), battery energy storage systems (BESSs), photovoltaic cells, diesel engines, wind energy conversion systems, fuel cells, etc. The MGDA is expected to improve the penetration ratio of renewable energy so that it will diminish CO2 emissions. A robust and efficient faults analysis program is needed to solve MGDA networks in real-time. The real-time asymmetrical faults analysis is oriented toward applications in the operations area rather than in planning analysis. The results of such asymmetrical fault studies can be used for microgrid distribution (MGD) adaptive relay coordination and settings when feeder reconfiguration is performed automatically.
Therefore, the present invention provides a method for analyzing and identifying a power flow asymmetrical fault of a microgrid power distribution system, and particularly for symmetrical and asymmetrical fault analysis, which is not limited by the three-phase and single-phase mixed situation. The application of the present invention is more practical.